Take husked coconut, bore out 1 of the "eyes" in the "monkey's face" you'll find at 1 end. Pour-out water. Refill nut with any white rum like new Cuban or Key West aguardiente, or inexpensive white Puerto Rican or Cuban rum - NOT brown or Jamaica. Cork tightly with a soft-wood peg driven-into the shell firmly. Bury in ground, dig-up after 6 month to a year. Drink the stuff neat, out of small glass.The process will add a ruddy amber color and a "most unusual and pleasant taste." Moreover, it will make the spirit more mellow the longer it stays in its tropical cask. Baker did give the option of cachaça later in the text.
For a method, I did end up using a hammer albeit later in the process. I used a 1/2 inch drill bit and made a hole in one of the eyes in each coconut. The wider the eye, the easier the bit went in for there was less tough, fibrous matter in the way. I then filled two with Seleta Cachaça and one with J.Wray & Nephew Rum. I did not realize until afterward that the directions specifically stated not to use Jamaican rum, but I now interpret that to mean dark aged and not white overproof Jamaican rum (which could stand a bit of mellowing). I sealed the holes with pieces of whittled tree branch and the recommended hammer. Instead of burying them, they are being stored in the kitchen for safe keeping.
I am curious to see if the rum will become coconut-flavored à la unsweetened Malibu or fat-washed with coconut oils. Only time will tell since Baker was rather vague about the effect.